Mixed ferrite compositions, including lithium ferrite



April 17, 1951 1. J. HEGYI 2,549,089

MIXED FERRIT COMPOSITIONS, INCLUDING LITHIUM FERRITE il? I 4 AVA ma ma vmw I VAVAVAVAV VAVAVAVAVAVAVV VWM@ /0006 M @WM '7 YAYAVAYAWV PM M Q@ Mc 'J- IIZ INVEN-roR IMRE d. HEB a0/E203 m71- ATToNEY April 17; 1951 l. J. HEGYI" 2,549,089

MxED FERRITE coMPosITxoNs, INCLUDING LITHIUM FERRITE Filed Deo. l5, 1948 2 Sheets-Sheet 2 A LA AWAvVAAyLWAvAvAvAvAvAvAvAv INVENTOR ATTO'RNEY Patented Apr. 17, W1951 MIXED FER/RITE COMPOSITIONS, INCLUDING LITHIUM FERRITE lImre J. Hegyi,`Pr`inceton, N. J., assigner to Radio Corporation of America, a .corporationzofDela- Ware Application December 15, 1948, `Serial'l\'lo.-65,1l32

(Cl. B52- 625) 13 Claims. `1

This inventionrelates to materials having improved magnetic properties. These materials may have unusually high values of magnetic permeability (c), or they may have desirably low loss values `(high Q factor) atradio frequencies, or a usefully high product of these two values.

The materials of the Vpresent invention vhave been `found to have unexpectedly high Q values and ,LQ product at high frequencies (3-30 megacycles). They exhibit unexpectedly high values of D. C'. resistance which can be controlled by varying the composition. `ln addition, they show a desirable reduction in drift compared to most previously known ferrites. el-Drift, as `used herein, is the term applied to decrease in ,i vwith time duringthe periodof measuring the properties of a sample.) They also have unexpectedly higher Curie-temperatures.

More particularly, the invention relates to improved materials of the class known Aas ferrites. The ferrites are cubic `crystalline materials containing FezOa and at least one other oxide, usually of abivalentmetal. Theferrites of the 4present invention may be Amade by the general method described inthe co-'p'ending application of H. W. Leverenz and R. L. Harvey, entitled Improvement in Magnetic Materials, Serial No. 776,292,

filed September 26, 1947.

' The present invention relates especially to the incorporation of lithium oxide, an oxide of a monovalentmetal, `in certain `tof the ferrite systems previously disclosed.

' Whenever Q values are mentioned throughout this specification, there is meant a numerical value `found bvdividing thevradio frequency reactancepby the resistance of a circuit in which the materialsof the present invention are introduced as induction coil core bodies.

By .mixed crystal ferrite is meant a ferrite material comprising two or more single ferrites whichareunited-in solid solutionto form asingle homogeneous crystalline material.

One object of Vthe present Ainvention is to providenovel mixed ferrite compositions having improved magnetic properties.

Another object of the invention is to provide novel Jferrite materials having controllable and usefully :high values of magnetic permeability.

Another `object of the invention is to provide novel ferrite materials having unusually high Q factors, especially at relatively high frequencies.

Anotherfobject of the invention is to provide novel ferrite materials having unusually high values of LQ product at relatively high frequencies.

Another object of 'the invention is Vto .provide novel ferrite materials vhaving .desirable values :of resistivity.

`Another object of :the invention is to Aprovide novel ferrite materials having greatly improved permeability drift l characteristics.

Still another object of the present invention is to provide improved ferrite materials having Vunusually high Curie-temperatures.

These and other uobjects `will be more `readily apparent andthe inventionwill'be better understood with reference tothe following specification, including `the drawings of which,

Fig. l is `a graphical `'representation :illustrating values `of MQ product for various compositions in a MnO:ZnO:Fe2O3 system with `LiOHadded before crystallization vat 0 C. in oxygen, `values beingmeasured at 5 megacycles.

Fig. 2 is a plot of the same system and same compositions as shown in Fig. f1 with resistivity and c given `for each composition.

Fig. 3 is a plot of the same systemas shown in Fig. 1 but Withcrystallization carried outat V120()o C., and

Fig. iis a plot ofthe samecompositiorls shown in Fig/3 with values `of yresistivity `and c given for each composition.

Although the compositions which are a part of the present invention are different from those vdescriloed in thepreviously mentioned Ico-pending applicationySerial No."776,292, and also different from those disclosed inco-pending application, Serial No. 795,046, 0f H. W. Leverenz and I, J.

`Hegyi, filed December 31, 1947, the general method of preparation is the same as described therein. Optimum heating temperatures and times, however, zare not `necesarily fthe same.

Briefly, the 4general `method of preparation of the materials of the present invention includes milling each of .the `oxide ingredients to a flne state of fsubdivision, intimately mixing the powdered oxides, preferably forming `a compressed Abody of the mixture, heatingthe body in an oxidizing atmosphere within a temperature range of about 900:C. to about .1500. C.^for from 1 minute to 6 hours, and then cooling. Although rapid cooling is preferred to obtain productswith high- 3 the compositions if a heating time of about 1 to 3 hours is used with temperatures of 10001200 C. The reaction product which is formed in all cases is a composite, homogeneous, crystalline 4 been found possible to vary the molding pressure Widely. Pressures of 2,000 lbs. per square inch have been found to produce the same improved results as pressures ten times as great. Tembody of cubic structure Which does not have the 5 porary binders may also be used. In general, it same stoichiometric proportion of oxygen to methas been established that the pressure of forming als as is present in the mixture before heating, Vshould be sufficient to form a closely coherent but the exact proportions of the elements, espebody and the pressurev actually chosen may be cially oxygen, present in the products is not easiany one whichwill produce this result. 1y determined. l0 The reaction mixture may be compressed into The oxidizing atmosphere in which the heatkany desired shape such as cylindrical or toroidal. ing of the reaction mixture takes place may be Warping may be lessened by mixing a small persupplied by passing a stream of oxygen through centage of a lubricant such as stearic acid or a the reaction chamber. Less desirably, air may microcrystalline Wax with the ingredients before be used in place of oxygen. It is also possible to l5 compressing them. The lubricant Should prefforin products having improved magnetic pererably be one which will completely volatilize or Y meability and low loss by heating the oxides in burnavvay during the heating step. a neutral atmosphere, such as one comprising l rihe formed bodies are subjected to heat treat-V helium or nitrogen, butvthe improvement is not ment as previously described and then they are as great as when an oxidizing atmosphere is cooled. Optimum properties are uSuallB7 Obtained used. In generalyit may be said that a non-reby rapid quenching in ail` 01 Water but it may be ducing atmosphere is necessary. necessary in many cases to cool slowly toV avoid Instead of starting With the oxides themselves, the appearance 0f StreSSeS Which Will Cause fracit is possible to start with a mixture of metallic turlng. compounds Which are in other than the oxide One ilnDOitaht aSDeCt 0f the present invention form 1n which they arepresent in the reaction is the production of novel ferrite materials comproduct, provided these starting materials Will be DTiSing Vai'iOU-S PI'ODOitiOhS 0f lithium eiiite, changed to the desired oxide upon heating to the Zine eilte and manganese feiiite- Table I. betemperatures, times and atmospheric conditions lOW, ShOWS a nulnhei 0f examples 0f COmpOSitiOnS stipulated. For example, instead of starting with prepared-as above described. by mixing lithium agmixture containing Fe203, the iron may be in in the form of the hydroxide together with zinc the form of ferrous oxide or the magnetic oxide. oXide, manganese CllOXide and ferrie Oxide. provided that heating takes place in an oxidizing rheSe Compositions, in thev OI'm 0f Cen'lpieSSed atmosphere, and as the hydroxide, carbonate, etc., hedies, Were CrYStalhZed at l000 C.:jin OXygen. if either an oxidizing or a, neutral atmosphere .Measurements Were then made 0f their magnetic is present. The other metallic ingredients may Permeability (it), loss factor (Q) at ve megaalso be present initially as hydroxides, carbon- Cycles, and D--C- resistivity ih OhmS/Cm-l The ates, acetates, etc., if the proper reaction atmos- MQ product has also been lndeated in each case. phare is chosen. Y Some examples have been included in .which no Because of the brittleness of the reaction 40 lithium iS present, OI the Sake Of illustrating the products, compressed bodies of the reactants may improvement Which OCCulS When lithium iS addbe formed at -high pressures of, say, 20,000 lbs. ed. Examples have alSO been included ih Which per square inch. TheV compressed bodies may either ZnO or Mn02 or both have been omitted, also be formed by extrusion molding processes at in Order t0 ShOW hOW the :4Q Dleduet dI'OpS When much lower pressures. Although, in compression all three oxidesv (other than F5202) l are not molding, very high pressures are preferred, it has utilized. l 4 y ,j v TABLE I Y' Ingredient Composition Ccm ositicn for-plotting i Code p Q 5 l i d. c. lesis- No. p' Mos. "'Q htwty a Lion zno M1105 F5503 Mnorenoa 2110.115203 Lizorezo. n ems/Cm- .2 o .9 1.0 .9 0 .1 24 40 950 2.5M. .2 .1 .8 1.0 .8 .1 .1 54 47 2,558 1.2M. 1517-1..- 0 .25 .75 1.0 .75 .25 0 22 22 454Y 0.22 M. 1525-1-.. .5 0 .75 1.0 .75 0 .25 25 55 828 2.0 M. 1299-1--- .1 .25 .7 1.0 .7 .25 .05 94 Vv40 4,505 1.0M. 1295-1--- .5 .15 .7 1.0 .7 .15 .15 7o 50 4, 520 7.3 M. 1297-1--- .5 .05 .7 1.0 .7 .05 .25 51,V 55 1,785 1.5M. 1524-1--- .8 0 .5 1.0 .5 0 .4 20: 35 700 0.58 M. m.-. .1 .55 .5 1.0 .5 .55 ,.05 129 59 5, 051 1.1 M. 1287-2-.. .3 v.25 .5 1.o .5 .25 .15 118 f 70 8,250 1.5 M. 1288-2-.. .5 .15 .5 1.o .5 '.15 .25 58 34 5, 552 1.5 M. 1500-1--. .5 0.1 .5 1.0 -.5 .1 .5. 72 l3o 2,150 0.75M. 1518-1--. 0 .4 .5 1.0 .5 .4 0V 7.5 10 75 0.5 M.

.1 .4 .55 1.0 .55 .4 .05 55 4,500 .2 .35 .55 1.0 .55 .55 .1 157 55 10,554 1.8 M. .5 .5 .55 1.0 .55 .5 .15 147 55 9, 555 9.1M.- .4 .25 .55 1.0 .55 .25 .2 125 f 52 5,500l 5.5M. 0 .5 .5 1.0 .5 .5 0 2.5 11 1 25Y 1.1M.. .1 .45 .5 1.0 .5 .45 .05 191 20 5,820 1.5 M. .2 .4 .5 1.0 .5 5.4` .1 179 59- 10,551 4.5M. 1290-2--. .5 .55 .5 1.0 .5 .55 .15 159 k71 11,551 4.5 M. 1505-1--. .5 .5 .5 1.o .5 .5 .2 143 4a 5,149V 1291-2-.. .5 .25 .5 1.0 .5 .25 .25 159 42 5, 855 5.5 M. 1292-2.-. .7 .15 .5 1.0 .5 .15 .35 58 45 2,494 1.0 M. 1507-1.-- .8 .1 .5 1.0 .5 .1 .4 28 50 1,400 1825-1--. 1.0 o .5 1.o .5 Y o .5 7.5 57 270 2.7 M. 1508-1--- .2 .45 .45 1.o .45 .45 .1 174 52 9,048 9.1 M. 1509-1 .4 .55 .45 1.o .45 Y .5 2 44 8,404 2.7M.V

`from 1 minute to 6 hours.

TABLE I--COntinued attache Ingredient Composition Composition for plotting (Ilide QM@ 5 Q dIesxso. l es.

Lion zno Muo. Flot Mnorao. znorezc. moreno. Ohms/m 1320-1-.- 0 .6 .4 `150 .14 .6. 0 41.3 19 2 5 1.7 M. 1293-2... .1 .55 .4 1.o 4 .55 1 .05 1'49 1o 1, 49o 3.3 M. 1294-2--- .3 .45 4 l. 0 .4 .45 15 252 30 7, 560 8.2 M. 1295-2 .5 .35 .4 1. 0 4 35 25 179 51 9, 129 1.8 M. 1310-1--- 1.0 .1 .4 1.04 .V4 ..1 .5 23 49 1,127` 1.5 M. 1326-1. 1. 2 0 .4 1. 0 ..4 0 6 48 3 4 163 7.3 M. 1311-1.-. .1 .6 .35 1.0` .35 .6. .05 141 5 705 316 M. 1312-1- .4 .45 .35 1.0 .B5 .45 2 265 38 10,070 2.7 M. 1313-4-- 8 25 35 .1. 0 .35 25 4 59 62 3, 658 1.4M. 131471- .3 55 ..3 .1.o .3 .55 15 335 `5 1. 675

1315-1- .6 .4 3 1. 0 .3 .4 3 140 52 7, 280 1.5 M. l321-l- 0 (.75 .25 .1'. 0 .125 .75 0 1.52 .'20` 24. `2.9 M. 1327-1--- 1. 5 0 .25 1. 0 .25 0 75 2.8 30 '84 1333-1-.- .3 .65 .2 1.0 .2 .65 .15 73 3 219 7.3 M. 1334-1.-. .8 .4 .2 1..() .2 .4 46 45 2,070 9.1 M. 1335-1- 1. 3 .1'5 2 1. 0 '."2 .15 65 6 40 240 9.1 M. 382--.- 0 1.0 .0 `1`. 0l 0 1.1)` 0` 1.01 24 24 90 M. 1328-1--. .5 75 0 1.0 0 75 .25 1. 03 Y 22 A 23 18 M. 1329-l .8 .6 0 1.,() 0 .6 .4 1.2 20 24 20 M. 1330-11-.- 1.0 .5 0 1.,'0 0 .5 .5 9 15 135 18 M. 1331-1" 1'. 2 .4 0 1.'0 Y .0 4 .6 5.,? 27 154 30 M. 1332-1--- 1. 5 .25 0 1.10 0 .25 .75 2.0 26 52 32 M. 1411-710- 2.0 0 .0 .1.0 0 0 V1. 0 1. 01 274 24 3.7 M. 679-10--- 0 0 1.0 1.`0 1.0 0 0 1.01 24 24 1.1 M.

Forfesistivicy K=1o3 and Mami.

The compositions listed `in Table I have been plotted in Fig. 1. For each composition plotted in this figure, the ,LLQ product has also been indicated.

It will be noted that the data 'given in Table 1 have been expressed in `twodifferent Ways. Columns 2, 3, 4 and 5 give the ingredientsof each sample in terms of relative number of moles of the compounds which weremiied together. But, in orderlto simplify thegraphical presentation of a Quaternary system ona triangular plot,` the values given in Columns "2,13, Lland 5 have been converted to Values Which 1varee'xpressed as relative moles of eachlcorresponding ferrite. These latter values have been listedfin Columns 6, '7 and 8 and `are assumed to beltheapproximate proportions of Eeach ferrite present the finalproduct.

Complete data, from which the examples listed in Table I have been chosen, show that useful improvementsin ,1Q productiare obtainedlwhen compositions are made up comprising about 0.01 to 'about 32.5mole per centlLigO, about 2.5 to about mole per cent Z'nO' and about 10 to about 42.511101@ per cent M1102. `.flltlfiough all of the tabulated examples are directed to compositions containing imole per cent iFe'zOs for lthe sake of comparison, experiment has shown that the FezOa content may be varied between about 30 and about mele per cent.

Fromian inspection of the values of Q product plotted on Fig. 1, an area will be noted in which the values are exceptionallyhigh. Y -This-areamay consisting of ZnO andCdO--lO to25 mole'per cent. `This is to be taken as the preferredrange of compositions. Preferred timefof heatin'gat this temperature is 3 hours, although it may be These values'fare found at relatively high frequencies of A3-30 megacycles.

Within the preferred range an optimum com- "position is foundcomprising FezOs-o mole per corresponds to 'a 'product having the proportions MnO2.Fe2O3-50 mole per cent, ZnO.Fe2O3-35 mole per cent and Li2OFe2O3-15 mole per cent.

The best range of compositions to produce products having highest-resistivities and useful values of n Vis -Fe2O3-50 fmole per cent, MnOz- 15 to 35 mole'percnt, ZnO (or CdO, or both togetherr-T to S25-mole per cent and Liao-2.5 to 12.5 mole per cent. On Fig. 1, this corresponds to a product compositioniof MnOz-SO to 70 mole per cent, ZnOF'eOs-lto 65 mole per cent and LizOFezOsto'25 mole per cent. Crystallization shouldtake Aplace lat 950-1250 C. and the preferred time'is about 11/2 hours, although this may also range from 51 minute to 6 hours..

Fig. 2 is aplot'of most of the same compositions shown in Fig. 1 but, in'this case, the resistivity and permeability values are given for each composition. The values Ain this gure show that `the D.C. resistivity of jthe materials can be controlled by Varying the LizO content of the reaction mixture; Materials having high D.C. resistivity are useful in various types of apparatus. For example, in some applications, two or more coils are wound on the 'same ferrite, with one coil having a higher D.'C. voltage than the other. In such a case, to be able `to wind the coil directly upon the ferritewithout the addition of an insulator between the ferrite and the coil, the ferrite must have high resistivity. Also, When a ferrite core must be mounted directly upon a chassis, -it-is advantageous that it have a high resistivity.

In the above described ferrite system, itislpossible to substitute Cd() forsome 'or' allof the `Zn() and obtain materials having unusually high values 'A of magnetic permeability, high Q factor and high D.C. resistivity. Table -II shows some Aexamples "of this type of composition and measured values of ,5, Q at 5 megacycles and D.C. resistivity. In `some instances, the ZnO was completely replaced by CdO, While in other'examples the compositions contained both ZnO and CdO. It has been concluded from a more complete set of measure- `ments that the compositions may contain the same mole percentagesof CdO as found for ZnO or that the percentage given for ZnO may be {ldivided'in any ratio between CdO and ZnO.

TABLE 1I [Crystallized at 1000" C. in oxygen] v. D G Ra- Code No. ZnO.Fe2Oa CdO.Fe2Oa LizOJezOe Mn0.Fez0s n Q @5mcs. pQ sistivlty,

ohms/e111.a

1517-3. 0 0.5 0 0. 5 1.4 18 25 470 K. 1518-3. 0 0. 4 0. 1 0. 5 Y 292 17 5, 264 360 K. 1519-3- 0 0.35 0. 15 0. 5 262 34 8, 909 5 M. 1520-3- 0 0.3 0.2 0. 5 198 40 7, 920 11 M. 15213 0. 1 0.25 0. 15 0. 5 230 42 9, 660 18 M. 1522-3- 0. 175 0.175 0. 15 0. 5 234 48 11, 232 9 M.

233 0.25 0. l 0.15 0. 5 V230 52 1l, 960 22 M.

Table III gives a number of examples of the same ferrite system MnO:ZnO (or CdO, or ZnO and CdO) Li2O:Fe2O3 with crystallization being and 4, Figure 3 giving the ,LQ product of each composition and Figure 4 giving the D.C. resistivity and permeability values.

TABLE III MnO:ZnO:Fe2O3 system with LiOH addition (bee ,fore crystallization Aat 1200 C. in orcygen) D. C. Re Code No. MnO.Fea05 Zn0.FenOa Liz0.FeaOa n Q 5 mcs. pQ sistivity,

l ohms/cm.s

. 9 1 338 5 `1, 690 1.12 K. 8 1 1 146 15 2, 390 0.23 M. .75 25 0 463 3 l, 389 1.0 K. 75 0 25 76 23 1, 748 6.9 M. .7 .05 25 82 25 2, 050 3.8 M. .7 .15 15 155 20 3, 100 0.75 M. 7 25 05 318 5 1, 590 22 K. .6 4 0 530 z 3 1, 590 280. 6 35 05 373 5 1,865 19.5 K. 6 25 15 202 20 4, 040 1.3 M. 6 15 25 112 27 3,024 5.5 M. 6 1 3 91 27 2, 457 4.5 M. .6 0 4 36 25 900 3.6 M. 55 4 05 404 5 2, 020 20 K. 55 35 10 313 11 3, 443 0.19 M. 55 30 15 228 22 5, 016 2.7 M. 55 25 20 190 28 5, 320 4.0 M. 5 5 0 540 3 1, 620 310. 5 45 05 407 5 2, 035 28 K. 5 4 1 322 10 3, 220 250 K. 5 35 l5 262 19 4, 978 1.3 M. 5 25 25 0.73 M. 5 15 35 3.6 M. .5 0 .5 19 27 513 3.6 M. 45 45 .1 342 5 1, 710 .45 3 2 232 22 5, 104 7.3 M. .4 6 0 33 2 66 210. 4 55 05 31 K. 4 45 15 328 5 1, 640 4.0 M. .4 35 .25 192 18 3, 456 3.3 M. .4 .1 .5 21 36 756 8.2 M. .4 0 6 10 25 250 4.5 M. .35 6 05 488 5 2, 440 22 K. 35 45 2 277 5 1, 385 4.5 M. 35 25 .4 61 1,891 5.5 M. 3 Y. 55 15 427 2 854 4.0 M. 3 4 .3 169 10 1, 690 3.8 M. 25 75 0 1. 1 22 Y 24 230. 25 0 75 6 20 120 2 .65 15 175 3 525 8.2 M. .2 4 4 89 5 440 0.79 M. 2 15 65 11 25 275 7.3 M.

Table IV is the corresponding table for compositions containing CdO either partiallyo'r Wholly substituted for ZnO. As in the case of compositions prepared at 1000 C., it has been found 0 that when prepared by heating et 12oo c., eedmium oxide may be substituted for zinc oxide either partially or totally and in any ratio` TABLE IV [Crystallized at 1200 C. in oxygen] D C. Re-

Code No ZnO.Fe2O3 CdO.Fe2Oa LiuOJenOa MnO.Fez0 p Q 5 mcs. LQ sstivity ohms/em.t

1517-1. 0 0.5 V0 0. 5 540 2 1, 080 150. 1518-1- 0 0. 4 V0. 1 0. 5 338 3 999 34 K. 1519-1 0 0. 35 0. 15 0. 5 245 18 3, 610 580 K. 41520-71 0 0. 3 0. 2 0.5 203 `23 4, 669 1.3 M. 1521-1- 0. 1 0. 25 0. 15 0. 5 242 20 4, 840 1.3 M. 1522-1..- 0. 175 0. 175 0. 15 0. 5 245 23 5, 635 1.8 M. 1523-1. 0. 25 0. 1 0. 5 0. 5 251 25 6, 275 3.3 M.

TABLE VII BeO:ZnO:MnO:Fe2Os with LiOH addition (before crystallization at 1200 C. in oxygen) A 1n Code No. Lion Bec Z110 M1101 Faoa Q t Q 2 $111 1 IDCS. utes Per cent 05 .20 .25 1 416 78 32,458 -1. 1 .02 05 .20 .25 .5 441 73 32,193 0. 5 04 05 20 25 5 463 70 32. 410 O. 6 08 (l5 20 25 5 441 80 35, 280 -0. I 0 075 175 25 5 393 85 35, 405 l. 5 02 075 175 25 5 396 82 34. 472 1. l 04 075 .175 .25 .5 413 78 33, 014 -0 `9 .08 075 175 .25 5 1 396 j 96 35,016 -0 2 Another category in which unexpected improvement has been found by adding Liz'OFezO tothe MnOFezOazZnOzFezOa system is that of controlling the Curie-temperature of the product. The Curie-temperature is the temperature at which the initial permeability has fallen to a slight fraction of approximately 1G of the maximum Value. It is of great advantage that the Curie-temperature of any of the ierrites which are to be used as core materials be far above room or other ordinary operating temperature so that a Vchange in temperature will not cause a relatively large' change in permeability.

Table VIII, below, shows the Curie-temperatures of a number of examples of ferrites in the System MnO.Fe2032Z110.Fe203Li20.Fe203.

usually an optimum heating temperature, how-` ever, for each composition.

I claim as my invention:

1. A cubic crystalline ferrite material consist-l ing essentially of the reaction product producedv 30 mole per cent of at least one oxide from the` class consisting of ZnO` and CdO and about 10V to about 42.5 mole per cent of MnOz.

2. A ferrite material according to claim 1 in which said heating temperature is from .1000-v TABLE VIII Crystalli" "C' zatiou ure' Code No. MnO.FenOa Z110.Fea03 L12O .Fe10a Tempem `Tempertme ature v o C. 1 `o C.- z .35 .45 .2 1000 280 .4 .55 .05 1000 145 .4 .45 .15 1000 28s .5 .5 o 1200 280 .5 .45 1 .05 1000 185 .5 .4 .1 1000 250 .5 .35 .15 1000 342 .5 .3 .2 1000 '38s .5 .4 0 1200 217 .0 .35 1 .05 1000 210 .0 .25 .15 1000 375 .7 .25 1 .05 1000 201 7 .15 15 1000' 419 1 These examples show that the Curie-tempera- 1200 C.

ture is raised when LizOFezOs is added to the Mn-Zn ferrite system. Although only a few examples out of `a large number have been tabulated, complete data indicate that a rise in Curietemperature is .obtained by adding .the same proportions of -'LiaO "and using the same proportionsof the other ingredients set forth in. the previous .definition of the limits of the compositions.

There have thus been described improved ferrite materials exhibiting unexpected improvements'in severalof their useful magnetic properties. proportions of the ingredients used should, in general, be Within the percentage ranges given since use of other proportions results in products which eitherfare not signicantly improved or are in'- ferior to previously known ferrites.

A range of time and temperature of heatinghas also been given. The size of the body influences the time necessary to bring about a complete Are action ofthe oxides. Very small bodies require mucnjshorter heating times than largebodies.V Also, the required time of heating isusually-Ain in v There 1s verse ratio to the temperature used.

The .i

3. A ferritematerial according to claim 2 in.

which said 4atmosphere is an oxidizing atmosphere.

4. A ferrite material according to claim 1 in which' the reaction mixtureincludes also from` about 0.2 to about 50 mole per cent BeO.

5.' Afeitrite` 'compositicn accordingto claim 1. inwhich saidl heating temperature 'is 10005 C.. and the ingredients of the reaction mixture arel present in the following proportions: Ferozmole per cent, Li2O-2.5 to 12.5 mole per cent,

MnO2-15 to 35 mole per cent and at least oney oxide from the `class consisting 01.2110 and CdO-10 to-.25 moleper cent. y

Y .An. article of manufacture characterized by having a relativelyhigh value of ,LQ product,4 said article being a compressed body of mate. rial having a predetermined shape, said rnate'l rial consisting essentially of a reaction product produced by heating together at temperatures A study oi' the above given data leads one to the conclusion that, if LiOH is not added to these ferrite systems, the optimum permeability in) :is

l MnOfl` and -Fez03. CdO can be substituted for part or "all of the ZnO. In these examples, crystallization v,was :carriedtoutat 1200 C. in oxygen.

TABLE V BeO.:ZnO:M1LO:FezOz with Lz'OH addition (before crystallization at '1200 C. in oxygen) attained using a crystallization temperatme 'of 1200 C. However. wheniLiOH 'is 'addedy Optimum #Q products .are produced usine a crystallization temperature of 1000 C. Higher ,MQ products are observed even though the value of .drops somewhat with increasing amounts of LiOH added to the composition, for the value of Q rises rapidly enough to more than compensate for the diminishing value of a.

'In Asorne uses, however, vthe -Q factor of a material may not be as important as its magnetic permeability o1' its D.C. resistivity. For such uses,the preferredtype of composition in the system of this aspect ofthe present invention would be that in which crystallization is carried outat 12U0 C. since `highervalues of both aand D.C.

Although 'only 'a `:few 'selected examples have been given y data 'indicate that lithium may be present as. LizO in the `proportion of about .01 to 'about32:5 mole lper cent, BeO may be used in the proportion of 'about 0.2 to about 50 mole per cent, Feza may be present in the proportion of about to about 7.0 mole per cent and the remainder may be either ZnO, CdO or any ratio of both. Ingeneral, the proportions (for all except Li20`) are the same as those disclosed inthe above men"- tioned co-pending application, Serial No. 795,- O46.

Table VI gives examples of ferrites Vprepared from the -same vmaterials as given in Table V but crystallized at 1l00 C. in oxygen.

TABLE vi BozznaMwocr-ezos with Lz'oH addition (befare crystallization at 1100* C.V in oxygen D C. Re- Code No. LiOH BeO ZnO MnOz FezOa u Q 5 mcs ,iQ sistivit f ohms/cm1 0 05 i 20 25 5 180 2 360 .025 025 20 25 5 264 7 1, 848 62.7K .05 025' 2 20 25 5 343 17 5, 831 91 K `0 e. 10 15 25 5 91 2 182 05 05 15 25 5 223 26 5, 79S 52.8 K'. l 05 15 25 5 235 37 8, 695 291 K. '0 15 i 1 25 .5 27 30 810 .05 1 1 25 .5 108 34 3, 672 63.5 K. l O5 1 25 5 156 36 5, 610 106 K. .`2 05 1 25 .'5 143 45 6, 435 6.26 M.

resistivity may be obtained using this temperature.

` It is alsol evident, from a study of the above given data, that, byadding LiOH (or its equivaient amount of LizO) t0 the given v.ferrite ma` terial pre-mix, there can be obtained a mag. netic'materal with controllable and higher Q factor and. #Q Product and also a material having controllable and higher D.C. resistivity. In these respects, materials are produced which are unexpectedly superior to manganesev ferrites, manganese-zinc ferrites, lithium ferrites or lithium-zinc 'ferrtes In another cci-pending application of H. W. Leverenz and I. J. Hegyi, Serial No. 795,046, led December 31, 1947, there have been disclosed ferrite compositions made from beryllium oxide in addition to zinc oxide and/or cadmium oxide, and manganese oxide. It has now been found that, when LiOH is added to these compositions, materials are produced having improve-d MQ products and higher D.C. resistivities. Table V, below, gives a few examples of ferrite compositions made from various mixtures of LiOH, B20. ZnO.

The above examples show that when LiOH (or the equivalent amount of LizO) is added to the system BeO:ZnO:MnO2:Fe2O3, a controllable increase .in LQ product may be obtained in the crystalline ferritewhich is produced. CdO may, as before, be substituted for part or all of the ZnO. Y

Many of the Previously prepared ferrites exhibit 'an instability of certain of their magnetic properties which greatly detracts from their use-y fulness. For example, they often exhibit a phef nomenon known as drift which is the term applied to a decrease in a which occurs over the period of time that the magnetic permeability is being measured. Drift is usually more pronounced at lower frequencies of, say, the order of 0.5 megacycle. It has been found that when lithium ferrite is added to certain of the ferrites which exhibit drift the drift is decreased. Examples of this property are shown in Table VII, below, for systems of crystalline ferrites made up by adding yLiOl-I to mixtures of BeO:ZnO (or CdQ, or both Zn() and CdO) :1\ln02:Fe2Oa. crystallization was at 1200 C. in oxygen.

in the 'above table, more complete Y about 2.5 to about 30 mole per cent of at least one oXide from the class consisting of ZnO and CdO, and about to about 42.5 mole per cent M1102.

7. An article according to claim 6 in which said temperatures are 10001200o C.

8. An article according to claim 7 in which said atmosphere is an oxidizing atmosphere.

9. A method of forming a core body having a relatively high value of MQ product comprising preparing an intimate mixture consisting essen tially of stoichiometric proportions of FezOa, LizO, M1102 and at least one oxide from the class consisting of ZnO and CdO, compressing said mixture to form a coherent molded body of predetermined shape, subjecting said molded body to a temperature of 9001500 C. in an oxidizing atmosphere to form a homogeneous cubic crystalline ferrite material and cooling said body.

10. A method of raising the Curie-temperature of a cubic crystalline ferrite body consisting essentially of manganese ferrite and at least one of a class consisting of zinc ferrite and cadmium ferrite, comprising incorporating therewith from 0.02 to 65 mole per cent oi' lithium ferrite.

11. A. homogeneous cubic crystalline ferrite body consisting essentially of about `0.02 to about i4 65 mole per cent lithium ferrite, about 5 to about 60 mole per cent of a ferrite from the class consisting of cadmium ferrite and zinc ferrite and about 20 to about 85 mole per cent manganese ferrite.

12. A homogeneous cubic crystalline ferrite body having relatively high Q product at 3-30 mega-cycles consisting essentially or" about 50 mole per cent ,MnOtFezOa mole per cent ZnOFezOa and 15 mole per cent LizOFezOa.

13. A homogeneous cubic crystalline ferrite body having relatively high resistivity consisting essentially of the reaction product produced by heating together at 950-1250 C. for from 1 minute to 6 hours in an oxidizing atmosphere FezOamole per cent, MnO2-el5 to 35 mole per cent, at least one oxide from the class consisting of Zn()` and CdO-7.5 to 32.5 mole per cent and Liso-2.5 to 12.5 mole per cent.

IMRE J. ll-IEGYI.

REFERENCES CITED The following references are of record in the file of this patent:

Kawai, Journal of the, Society of Chemical Industry, Japan, vol. 37, No 4, 1934; page 174B. 

1. A CUBIC CRYSTALLINE FERRITE MATERIAL CONSISTING ESSENTIALLY OF THE REACTION PRODUCT PRODUCED BY HEATING TOGETHER IN A NON-REDUCING ATMOSPHERE AT TEMPERATURES OF FROM ABOUT 900* C. TO ABOUT 1500* C. FOR FROM ABOUT 1 MINUTE TO ABOUT 6 HOURS AN INTIMATE MIXTURE OF ABOUT 30 TO ABOUT 70 MOLE PER CENT FE2O3, ABOUT 0.01 TO ABOUT 32.5 MOLE PER CENT LI2O, ABOUT 2.5 TO ABOUT 30 MOLE PER CENT OF AT LEAST ONE OXIDE FROM THE CLASS CONSISTING OF ZNO AND CDO AND ABOUT 10 TO ABOUT 42.5 MOLE PER CENT OF MNO2. 